1. Field of the Invention
The present invention relates to an optomagnetic (magneto-optical) disc apparatus which is capable of erasing and writing information on an optomagnetic (magneto-optical) disc, and in particular, to an optomagnetic (magneto-optical) disc apparatus which is capable of effecting so-called overwriting by the modulation of a magnetic field using a floating type magnetic head.
2. Related Background Art
In general, conventional magnetic-field modulation type optomagnetic disc apparatuses are provided with an optical pick-up 100, a magnetic head 11 and a mechanism for retreating or removing the magnetic head 11 from its operative position, as is shown in FIG. 1. In this optomagnetic disc apparatus, an optomagnetic disc 105 having an optomagnetic medium layer and a protective layer formed on a transparent substrate and contained in a disc cartridge 106 can be loaded onto a turn-table (not shown). Below the loaded disc 105, namely, at tile transparent substrate side of the disc 105, the optical pick-up 100 mounted on a carriage 103 is arranged, and above the loaded disc 105, namely, at the protective layer side of the disc 105, the magnetic head 11 mounted on the carriage 103 is disposed at a position opposite to an opened shutter portion of the disc cartridge 106. At this position the magnetic head 11 is also located opposite to an objective lens of the optical pick-up 100.
The carriage 103 is movably supported by bearings 101 and so forth along a slide guide (not shown) that extends in a radial direction of the optomagnetic disc 105. The carriage 103 can be moved by a linear motor 102 along a track extending in the direction of the optomagnetic disc 105.
In the structure of the floating type slider for supporting the magnetic head 11, a leaf spring 10 that acts as a load beam is mounted to an intermediate member 12 and the magnetic head 11 is fixed to a tip portion of the leaf spring 10. The intermediate member 12 can be pivotally supported by the optomagnetic head carriage 103 through a shaft 13 as shown in FIG. 1, or the intermediate member 12 can be movably supported in the upward and downward directions by a magnetic head carriage 210 which can be moved independently of the optomagnetic head carriage 103 as shown in FIG. 2.
The magnetic head 11 is moved upward by a retreating means when the disc cartridge 106 is being loaded or unloaded. In the structure of FIG. 1, the leaf spring 10 and the magnetic head 11 are moved by moving a guide roller 15, located on the intermediate-member 12, upward or downward using a solenoid mechanism (not shown) or the like.
The leaf spring 10 functions to resiliently push the magnetic head 11 against the disc 105, and its spring constant is set to a small value to reduce the fluctuation of the spring force or pushing force due to the surface fluctuation of the disc 105. Therefore, the amount of deformation (i-e., the amount of the push) of the leaf spring 10 itself needed to generate a desired spring force is set to about 2-4 mm. Thus, in order to bring the magnetic head 11 from a free state (a state in which the magnetic head 11 is apart from the disc surface) to the above-mentioned pushing state, the leaf spring 10 must be pushed in the spring force direction by about 2-4 mm after the floated surface of the magnetic head 11 comes in contact with the surface of the disc 105.
In the above structure, when the magnetic head 11 is to be moved away from the disc cartridge 106, the intermediate member 12 is rotated about the shaft 13 by pushing down the guide roller 15 In the case of the structure shown in FIG. 2, a guide roller 15 is elevated to move the magnetic head 11. At this time, the leaf spring 10 in the retreated position is deflected towards the disc 105 by a predetermined amount .DELTA.h due to the weight of the leaf spring 10 and the magnetic head 11. Therefore, determination of a rotation angle .theta..sub.b of the intermediate member 12 and a stroke amount b of the movement of the guide roller 15 must account for the amount .DELTA.h of the deflection of the leaf spring 10. Thus, when the magnetic head 11 is moved away from the surface of the disc 105 by a distance h, the stroke amount b of the movement of the guide roller 15 effected by the solenoid, etc., becomes larger by an amount corresponding to the amount of the deflection .DELTA.h of the leaf spring 10. This results in a need for a large-sized mechanism which includes the solenoid.